<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 600px;
            margin: 100px auto;
        }

        .message{
            display: inline-block;
            font-size: 12px;
            color: #999;
            padding-left: 20px;
        }
        .wrong{
            color: red;
        }
        .right{
            color: green;
        }


    </style>
</head>
<body>

    <div class="register">
        <input type="password" class="ipt">
        <p class="message">请输入6~16位密码</p>
    </div>

    <script>

        var ipt = document.querySelector('.ipt');
        var message = document.querySelector('.message');

        ipt.onblur = function() {
            if(this.value.length < 6 || this.value.length > 16){
                   message.className = 'message wrong';
                   message.innerHTML = '您输入的位数不对！！！';
            }
            else{
                message.className = 'message right';
                message.innerHTML = '输入正确';
            }
        }

    </script>
    
</body>
</html>